1. Field of the Invention
The present invention relates to an inkjet recording apparatus for forming images by discharging ink as ink droplets from an inkjet recording head (ink discharge head) onto a recording medium, and more specifically to an inkjet recording apparatus which can prevent air bubbles that have accumulated upstream of a filter from flowing into the ink discharge head by disposing the filter for removing foreign matters in an ink supply channel between an ink tank and an ink discharge head.
2. Description of the Related Art
Conventionally, one known example of an image recording apparatus is an inkjet recording apparatus (inkjet printer) that has an inkjet head (ink discharge head) with an alignment of multiple nozzles, and that forms an image on a recording medium by discharging ink from the nozzles while moving the inkjet recording head and the recording medium relatively to each other.
Various methods for discharging ink in inkjet printers are conventionally known. One known example is a piezoelectric system, wherein the volume of a pressure chamber (ink chamber) is changed by deforming a vibration plate that constitute part of the pressure chamber due to the deformation of a piezoelectric element (piezoelectric ceramic) so that the ink supply and the ink discharge to the pressure chamber are controlled. The other known example is a thermal inkjet system wherein ink is discharged by the expansion energy of the air bubbles created by heating ink.
According to an image recording apparatus that has an ink discharge head, such as an inkjet printer, ink is supplied from an ink tank that accumulates ink to an ink discharge head via an ink supply channel, and the ink is discharged from the ink discharge head by the discharge methods described above. However, air bubbles might form in the ink when the ink is supplied from the ink tank to the ink discharge head. When the air bubbles form in the ink, the air bubbles flow into the ink discharge head, so that the recorded image is missed due to a decrease of ink concentration and a failed discharge. Therefore, there is a problem according to degrade the quality of the recorded image.
In order to resolve the above problem, a known example of the inkjet recording apparatus conventionally comprises a filter member for removing foreign matters disposed in an ink supply channel which connects an ink cartridge and a recording head, and opposing surfaces of the filter member include the deforming members capable of displacement toward the filter member. Therefore, when the surfaces are pressed and deformed by an operating member, the air bubbles remaining upstream of the filter member are discharged downstream of the filter member due to a strong ink flow created by reducing the effective area of the filter member (for example, see Japanese Patent Application Publication No. 2001-18414).
Similarly, another known example comprises a deforming member which deforms toward a filter member by providing negative pressure in vicinity of the filter member in an ink supply channel between an ink cartridge and a recording head (for example, directly upstream of the filter member). Therefore, since the deforming member is deformed to close off the space upstream of the filter member in which the remaining air bubbles are apt to accumulate, the remaining air bubbles are forcefully pushed downstream of the filter member and discharged (for example, see Japanese Patent Application Publication No. 2001-18419).
However, according to Japanese Patent Application Publication No. 2001-18414, since the filter member cannot be deformed largely, the effective sectional area of the filter member cannot be reduced by much. In order to increase the amount of deformation, the filter sectional area must be increased, but the ink speed passing through the filter member is reduced by increasing the filter sectional area. Therefore, there is a problem that air bubbles cannot be discharged by passing through the filter member along with the ink.
In addition, according to Japanese Patent Application Publication No. 2001-18419, the deforming member is deformed by negative pressure. Eventually, while the surface of the recording head on which nozzles are formed is sealed by a capping device, the negative pressure is utilized during the ink suction by a suction pump to prevent nozzle clogging due to the solidifying of ink. Therefore, there is a problem in which the air bubbles cannot be removed with arbitrary timing.